Of the 40 lives lost, 23, including two babies, have been buried in a mass grave near the scene of the accident, which occured at Asejire in Aiyedaade local government area of Osun state.
The accident involved six vehicles - one of them, a petrol tanker.
According to eyewitnesses, the petrol tanker lost control and rammed into oncoming vehicles, spilling its load which then caught on fire.
The Sector Commander of the Federal Road Safety Corps, FRSC, Godwin Oghagene, says recklessness was responsible for this accident, in which only five people survived unhurt.
According to statistics from the FRSC, over 32,000 people die in Nigeria due to road accidents very year.
Many such accidents are caused by recklessness of motorists, poor maintenance culture, bad roads and ineffective sanctions on those who cause accidents leading to deaths of their loved ones.